There is a continuing effort to decrease the weight mass of material used in packaging. As a part of this effort, substances that have been sold in bottles are now being sold in film pouch containers. This reduces the packaging weight to less than half of that of a bottle. There can be an additional savings if the liquid substance is concentrated prior to film packaging. In this way, the amount of film packaging required can be further reduced since the diluent is added at the time of use. However, a film must have specific properties in order to be effectively used for packaging. This is particularly the case when the film package is to be formed and/or sealed using radio frequency (RF) energy techniques. In RF sealing techniques, RF energy is used to soften the film sufficiently so that the film can be welded. This is an effective sealing technique since the two layers of film that are to form the pouch are heated to similar temperatures and can be welded. At the point of sufficient softening, but prior to any flowing of the film material, the two layers become welded. This provides for significant advantages over techniques that use adhesives or the heating of the film by conduction, i.e., through contact with a heated plate. It is also the case that RF energy provides for a more uniform heating and thus produces good seals.
Although RF energy provides for good seals, there are certain requirements with regard to the use of RF energy. The film must be capable of being heated using RF energy. That is, it must be able to be heated to near melt through contact with RF energy having a frequency of about 10 MHz (Megahertz) to 50 MHz. This is the frequency range most used for heating polymeric materials. Not all polymeric films can be effectively heated to produce good seals using RF energy. The plastic film used in the sealing layer must be bysular for RF sensitivity.
The films will also require other characteristics dependent at least in part on the substance that is contained in the pouch made from the film. It has been found that when a film is to contain a bleach that the film must have a transmissivity for oxygen since oxygen is evolved during the storage of bleach pouches. If this oxygen cannot be dissipated through the pouch wall, pressure will build-up in the pouches to the point that the pouches could possibly rupture. If this occurs, there would be a loss of product and possible damage to the surrounding area. In addition, it is desirable with many substances to have some of the aroma of the substance contained in the pouch be transmitted to the exterior. This provides a way to acquaint the customer with the fragrance of the product. Consequently, it is desirable for the film to have a partial transmissivity for fragrances.